The present disclosure relates to an optical body, an optical body manufacturing method, a solar shading member, a window member, an interior member, and a fitting. More particularly, the present invention relates to an optical body for directionally reflecting incident light.
Recently, cases of coating a layer partly absorbing or reflecting the sunlight on architectural glasses for high-rise buildings and housings, vehicular window glasses, etc. have increased. Such a trend represents one of energy-saving measures with the view of preventing global warming, and it is intended to reduce a load of cooling equipment, which is increased with solar energy, i.e., the sunlight, entering the indoor through windows and raising the indoor temperature.
Optical energy incoming from the sun is primarily provided by light in a visible range at wavelengths of 380 to 780 nm and light in a near infrared range at wavelengths of 780 to 2100 nm. Because transmittance of the light in the latter near infrared range through windows is unrelated to visibility of human eyes, the transmittance of the near infrared light is an important factor affecting the performance that is to be provided by a window having high transparency and a high thermal shielding ability.
As an example of methods for blocking the light in the near infrared range while maintaining transparency to the light in the visible range, there is a method of providing, on a window glass, an optical body having a high reflectance in the near infrared range. With regards to such a method, various techniques using, as reflecting layers, an optical multilayer film, a metal-containing film, a transparent electroconductive film, etc. are already disclosed (see, e.g., pamphlet of International Publication WO05/087680).
However, the reflecting layers in the disclosed technique are formed on a flat window glass, and the incident sunlight is just specularly (regularly) reflected. Therefore, the light incoming from the sky and specularly reflected by the flat window glass reaches other outdoor buildings and the ground where the light is absorbed and converted to heat, thus raising the ambient temperature. Accordingly, a local temperature rise occurs in the surroundings of a building in which all windows are coated with the above-mentioned type of reflecting layer. This gives rise to the problems that, in urban areas, a heat island phenomenon is accelerated and grass is not grown in areas irradiated with the reflected light.
To cope with the above-mentioned problems, a technique of using a directional reflector to retroreflect the incoming sunlight in the incident direction thereof is proposed (see, e.g., Japanese Unexamined Patent Application Publication No. 2007-10893). In the proposed related art, the directional reflector is constituted by arraying, e.g., many substantially pyramidal structures. Light incident on the directional reflector is reflected by surfaces of the substantially pyramidal structures plural times such that the light is eventually reflected substantially in the incident direction.
However, the function of the directional reflection is degraded for the light entering the directional reflector at a large incident angle. Further, although ridge portions of the substantially pyramidal structures are designed to have substantially triangular shapes in cross-sections, the actual ridge portions may have shapes deformed (collapsed) from the ideal shape in some cases for the reason encountered in manufacturing processes. In such a case, the incident light entering the ridge portions is reflected in the specular reflection direction without being reflected plural times. Thus, as the shapes of the ridge portions are deformed from the ideal shape to a larger extent, a directionally reflected component of the incident light is reduced.
Stated another way, the above-described directional reflector has the problem that, with the reduction of the directionally reflected component, the sunlight reaches the ground in a larger amount and causes a temperature rise near the ground surface.